Inverse beta decay in a nonequilibrium antineutrino flux from a nuclear reactor

The evolution of the reactor-antineutrino spectrum toward equilibrium above the inverse-beta-decay threshold during the reactor operating period and the decay of residual $\bar \nu _e $ radiation after reactor shutdown are considered. It is found that, under certain conditions, these processes can play a significant role in experiments seeking neutrino oscillations.     

Ion detection from beta decay and two-body decay experiments with laser-cooled atoms

Localized and cold samples of atoms produced with laser cooling and trapping techniques are a powerful tool for nuclear β-decay experiments. Recently we have concentrated on measurements of the momentum of the daughter ion produced, which leads to a variety of new observables. Angular distributions of the recoils with respect to the nuclear spin in β ⁺ decay are sensitive to non-standard model interactions. Measurements of the momentum of monoenergetic recoils from either electron capture or isomer γ decay would make it possible to search for particles with masses of 10s of keV.      

The beta decay of139I

With the⁹⁶Ru(⁵⁸Ni,2pn) reaction we produced¹⁵¹Yb₈₁ and studied its decay after online mass separation by γ-spectroscopic techniques. The decay populates the four positive parity single proton levels in the N=82 daughter nucleus¹⁵¹Tm and establishes I^π=1/2⁺ for the so far unknown¹⁵¹Tm low spin isomer. Using BCS theory proton single particle energies for¹⁵¹Tm were extracted from the observed excitation energies.     

The beta decay of176m Lu

The shape factors of the 1^?→2⁺ and 1^?→0⁺ beta transitions and theβ-γ directional correlation of^176m Lu have been measured. An analysis in terms of nuclear matrix elements is given.     

The Gamow-Teller beta decay of100Cd

Neutron-deficient isotopes of cadmium were produced in thep(600 MeV)+^natSn spallation reaction. The ISOLDE facility provided mass-separated beams of these isotopes. The production yield was 10³ to 10⁴ atoms/s for¹⁰⁰Cd and roughly two orders of magnitude less for⁹⁸Cd. The properties of the¹⁰⁰Cd→¹⁰⁰Ag decay were studied in detail by X-ray,γ-ray and conversion electron spectroscopy. Forty nineγ-transitions were assigned to this decay, and all but five of them were placed in the decay scheme. The half-life was determined to be 49.1±0.5 s. TheQ _EC value of 3890±70 keV was deduced from a comparison of experimental and theoreticalβ ⁺/(EC+β ⁺ probability ratios. Seven 0⁺→1⁺ Gamow-Teller transitions with log ft values between 3.5 and 4.9 were identified. The total (summed) strength is about five times smaller than predicted by the shell model for the transformation of ag _9/2 proton into ag _7/2 neutron. The quenching of the Gamow-Teller strength and other questions of nuclear structure are discussed for the¹⁰⁰Cd decay. The properties of⁹⁸Cd are inferred by extrapolation of^104,102,100Cd data, and some preliminary experimental results on⁹⁸Cd decay are presented.     

Double beta decay

Double beta decay is a rare nuclear process changing the nuclear charge by two units leaving atomic number unchanged. The detection of the neutrino accompanied mode (A,Z)→(A,Z + 2) + 2e^? + &;2v^? ₂ with half-lives around 10²⁰ years is among the rarest decays ever observed. Of outmost importance for particle physics and especially neutrino physics, is the neutrinoless mode (A,Z)→(A,Z + 2) + 2e^?. This process is violating lepton number by two units and requires massive Majorana neutrinos, i.e. neutrino and antineutrino are identical. The current experimental status is reviewed and an outlook towards future activities is given.     

Vacuum decay by inverse scattering

We discuss the decay of false vacua which originate from quantum mechanical effects. In particular we examine the $\text{1}\text{N}$ expansion of the O(N) λφ⁴ model. This model has an effective potential which is complex for large values of the field. In a previous paper we showed that this effective potential could not be used to calculate the decay rate directly. In the present work we show that the vacuum can decay via poles in the effective action which are evident when it is written in terms of scattering variables.     

Determination of the direction to a source of antineutrinos via inverse beta decay in Double Chooz

To determine the direction to a source of neutrinos (and antineutrinos) is an important problem for the physics of supernovae and of the Earth. The direction to a source of antineutrinos can be estimated through the reaction of inverse beta decay. We show that the reactor neutrino experiment Double Chooz has unique capabilities to study antineutrino signal from point-like sources. Contemporary experimental data on antineutrino directionality is given. A rigorous mathematical approach for neutrino direction studies has been developed. Exact expressions for the precision of the simple mean estimator of neutrinos’ direction for normal and exponential distributions for a finite sample and for the limiting case of many events have been obtained.     

The beta decay of neutron-deficient rhodium and ruthenium isotopes

The very neutron-deficient ^91,92,93Rh and ^90,91Ru nuclei were produced in ⁵⁸Ni(^36,40Ar, xn yp) fusion-evaporation reactions. Reaction products leaving the target were stopped in a gas cell and selectively laser ionised before mass separation using the LISOL setup. Data were collected in singles and coincidence formats to investigate -delayed and isomeric decays. Ground-state decays of ^91,93 Rh to excited states in the daughter nucleus were identified for the first time and the decay schemes of ^90,91 Ru were expanded. The low-spin isomeric decay of ⁹²Rh was identified for the first time and detail added to the decay scheme of the known high-spin state. Results are discussed in terms of comparison with shell model calculations. -delayed proton activity in the lighter ⁹⁰Rh and ⁸⁹Ru isotopes was also investigated and upper limits for this decay mode in these two nuclei have been included.Received: 26 November 2003, Revised: 12 January 2004, Published online: 10 August 2004PACS: 23.40.-s decay; double decay; electron and muon capture - 21.10.-k Properties of nuclei; nuclear energy levels - 21.10.Tg Lifetimes - 21.60.Cs Shell modelM. Górska: Present address: Gesellschaft für Schwerionenforschung, Planckstrasse 1, D-64291 Darmstadt, Germany.K. Van de Vel: Present address: VITO, IMS, Mol, Belgium.     

The beta decay of88gNb and88mNb

The level structure of⁸⁸Zr is investigated via the beta decay of^88g Nb and^88m Nb whose half-lives are measured to be 14.4±0.2 m and 7.7±0.1 m, respectively. The decay properties are studied by means of beta and gamma spectroscopy techniques. The level structure of⁸⁸Zr populated in the decays of both isomers is proposed with deducedJ ^π values. Theβ-decay energies for^88g Nb and^88m Nb are measured to be 7.55±0.10 and 7.59±0.10 MeV, respectively. The structure is discussed in terms of the shell model.     

Theoretical antineutrino detection,direction and ranging at long distances

In this paper we introduce the concept of what we call “NUDAR” (NeUtrino Direction and Ranging), making the point that measurements of the observed energy and direction vectors can be employed to passively deduce the exact three-dimensional location and thermal power of geophysical and anthropogenic neutrino sources from even a single detector. Earlier studies have presented the challenges of long-range detection, dominated by the unavoidable inverse-square falloff in neutrinos, which force the use of kiloton scale detectors beyond a few kilometers. Earlier work has also presented the case for multiple detectors, and has reviewed the background challenges. We present the most precise background estimates to date, all handled in full three dimensions, as functions of depth and geographical location. For the present calculations, we consider a hypothetical 138 kiloton detector which can be transported to an ocean site and deployed to an operational depth. We present a Bayesian estimation framework to incorporate any a priori knowledge of the reactor that we are trying to detect, as well as the estimated uncertainty in the background and the oscillation parameters. Most importantly, we fully employ the knowledge of the reactor spectrum and the distance-dependent effects of neutrino oscillations on such spectra. The latter, in particular, makes possible determination of range from one location, given adequate signal statistics. Further, we explore the rich potential of improving detection with even modest improvements in individual neutrino direction determination. We conclude that a 300 MW_th reactor can indeed be geolocated, and its operating power estimated with one or two detectors in the hundred kiloton class at ranges out to a few hundred kilometers. We note that such detectors would have natural and non-interfering utility for scientific studies of geo-neutrinos, neutrino oscillations, and astrophysical neutrinos. This motivates the development of cost effective methods of constructing and deploying such next generation detectors.     

The first forbidden beta decay of Pb209

The 9/2⁺→9/2^? first forbidden β-transition of Pb²⁰⁹→Bi²⁰⁹ has been investigated. The end point energy has been determined to (644.6±1.2) keV, the half life to (3.253±0.014) h. For the shape factor no deviation from the allowed form has been found within an accuracy of 1%. Shape factor andft-value can be excellently interpreted by the shell model injj-coupling.     

Double beta decay experiments

The present status of double beta decay experiments is reviewed. The results of the most sensitive experiments are discussed. Proposals for future double beta decay experiments with a sensitivity to the 〈m _ν〉 at the level of (0.01–0.1) eV are considered.     

The isospin mixing and the superallowed Fermi beta decay

In the present work, the isospin admixtures in the nuclear ground states of the parent nuclei and isospin structure of the isobar analog resonance (IAR) states have been investigated by studying the 0^?+???0^?+? superallowed Fermi ?? decays using Pyatov??s restoration method. Within the random phase approximation (RPA), in this method, the effect of isospin breaking due to the Coulomb forces has been evaluated, taking into account the effect of pairing correlations between nucleons.     

Neutrinoless double beta decay

The physics potential of neutrinoless double beta decay is discussed. Furthermore, experimental considerations as well as the current status of experiments are presented. Finally, an outlook towards the future, work on nuclear matrix elements and alternative processes is given.     

The pionic beta decay in chiral perturbation theory

Within the framework of chiral perturbation theory with virtual photons and leptons, we present an updated analysis of the pionic beta decay including all electromagnetic contributions of order e ² p ² . We discuss the extraction of the Cabibbo-Kobayashi-Maskawa matrix element |V _ud | from the experimental data. The method employed here is consistent with the analogous treatment of the decays and the determination of |V _us |. Received: 19 September 2002 / Published online: 24 January 2003     

Double beta decay and all that

This review illustrates the present state of knowledge and directions of interest in infrared spectroscopy through the discussion of a number of examples of recent work. After a brief introduction the survey falls into three parts. The first is concerned with problems of assignment and interpretation of the spectra of polyatomic molecules, and the calculation of force constants. The second deals with the study of some chemical systems by infrared methods, and in the final section mention is made of a number of specialized topics such as matrix-isolation techniques.